Electronic control apparatus

ABSTRACT

An electronic control apparatus applicable to a number of different actuatable structures of the type requiring a predetermined voltage level or current flow wherein the apparatus utilizes a decoding means having a plurality of current-carrying elements which are arranged in a manner so as to require simultaneous actuation in order to provide a desired enabling voltage or current flow for the structure with which the apparatus is connected. The apparatus is especially adapted for use as a lock for a system having an ignition coil for energy transfer between the windings of the coil can be effected only if the elements of the decoding means are simultaneously actuated.

United States Patent 72 inventor Raymond L. Fuess 3,208,042 9/1965 Haigh et a1 340 149 P. O. Box 9, Mountain View, Calif. 94040 3,271,629 9/1966 Holy ZOO/42X 3,403,380 9/1968 Welsh 340/149A 211 AppLNo. 769,890 22 Filed 0ct.23,l968 451 Patented Jan.5, 1971 [54] ELECTRONIC CONTROL APPARATUS 179lG; 317/1576, 157.61, 13.4; 340/149, 149A; 200/46, 48; 307/115, 252; 70/278 [56] References Cited UNITED STATES PATENTS 2,794,869 6/1957 Noregaard ZOO/42X F -l 6 E H -l? J Hi It -+5 1 n 1 5 0 -a: R l

. I, 6 P i'ii E L I SOCKET 1 COILLOCK ASSEMBLY T0 STARTER 96 RELAY INPUT Primary Examiner-Laurence M. Goodridge Attorney-Townsend and Townsend ABSTRACT: An electronic control apparatus applicable to a number of different actuatable structures of the type requiring a predetermined voltage level or current flow wherein the apparatus utilizes a decoding means having a plurality of current-carrying elements which are arranged in a manner so as to require simultaneous actuation in order to provide a desired enabling voltage or current flow for the structure with which the apparatus is connected. The apparatus is especially adapted for use as a lock for a system having an ignition coil for energy transfer between the windings of the coil can be effected only if the elements of the decoding means are simultaneously actuated.

PATENTED JAN 5 I9?! SHEET 1 UF 2 Has.

a 0 T N E V m W STARTER RELAY INPUT AHERNMOR RAYMOMQ L. FU E55 W YW,

mmms FIGZ PATENTEU JAN 5mm 3553.494

SHEET 2 0F 2 INVENTOR.

RAYMOND L.FUE3S BY ATTORNEYS ELECTRONIC CONTROL APPARATUS This invention relates to improvements in electronic control apparatus and, more particularly, to an electronic control apparatus utilizing direct current logic and being programmable in accordance with a preselected code.

While the present invention is suitable for a wide variety of different applications, it is especially suitable for use as an ignition lock for an internal combustion engine of a vehicle or the like. The advantages achieved by the use of the invention is that the lock can be constructed in accordance with a preselected code which is one of a relatively large number of codes from which an individual can choose. Thus, the teachings of the invention provide a structure which renders extremely difficult any theft of the property safeguarded by the apparatus when the latter is used as a lock.

Since the invention can be clearly understood when applied to the control of an ignition system, the following description, with reference to the accompanying drawings, will be made based upon an ignition system. for a conventional ignition coil in combination with breaker pointsoperated from the cam shaft of a vehicle or the like,

Among the advantages of the invention is that it may be operated by a key remote from the circuitry which provides the actuatingor voltage current signals. The invention uses AND and NAND logic preferably and the key for operating the apparatus can only be duplicated by extensive trial and error so as to discourage any would bethief. If the invention is used with the ignition system of a vehicle, the key must be removed to stop the engine, thus providing a security measure not capable of being achieved with conventional ignition keys. Wiring cannot be rearranged or cut to defeat the purposes of the lock. An alternative power source cannot be utilized to operate the circuitry.

The primary object of this invention is, therefore, to provide an improved electronic control apparatus of simplified construction and capable of utilizing digital logic as well as providing useful voltage or current signals levels for use as enabling means for permitting the actuation of any one of a number of different actuatable power structures.

Another object of this invention is to provide apparatus of the type described wherein the apparatus has programmable decoding means and an actuating member or key selected from a relatively large number of constructions for actuating the decoding means to provide useful voltage and current signals, whereby the apparatus is suitable for use as an electronic lock capable of giving an enable" or disable" command.

A further object of this invention is to provide control apparatus of the type described wherein the apparatus is capable of controlling the energy transfer between the windings of an ignition or other impulse-operated coil so that the apparatus can provide an additional safeguard against vehicle thefts as well as to permit a simplified, programmed device for an ignition which discourages the .keeping of the ignition key in the vehicle during periods of nonuse.

Other objects of this invention will become apparent as the following specification progresses.

in the drawings:

FIG. I is a schematic view of the apparatus when the same is used with an ignition coil or an ignition system; and

FIG. 2 is an electrical schematic of the ignition system showing the wiring between the various components of the system.

To illustrate the teachings of the present invention, the control apparatus forming the subject matter of this invention will be hereinafter described with respect to the control of an ignition system for an internal combustion engine wherein the ignition system for an internal combustion engine wherein the ignition system has an ignition coil 10 for generating a voltage and thereby an electrical current in the secondary winding 14 of the coil to create a spark for the various spark plugs of the engine according to the firing order of a distributor (not shown). The coil has a primary winding 12 inductively coupled with secondary winding 14, the primary winding 12 being in series with a ballast resistor 16 and a switch 18 defining the breaker points of the ignition system. Resistor 16 is connected to terminals through fuse 114 and switch 18 is connected to the negative battery terminal as represented by the electrical ground symbol.

The improvement of this invention is directed to a means for controlling the flow of current in a particular circuit and thereby the voltage level at a particular location so that this voltage level can be used to enable or disable the current flow through a circuit element connected to primary winding 12 to thereby either permitting transfer of energy between the windings of the coil or dissipating this energy in the circuit element, i.e., no energy transfer between the coil windings. In particular, the invention will be described with respect to controlling the forward and reverse bias voltage on the gate 26 of a silicon controlled rectifier or SCR 20 whose anode 22 and cathode 24 are connected in parallel with primary winding 12 as shown in FIG. 1. Gate 26 is coupled by resistors 29 and 27 to the collector terminal 30 of an NPN transistor 32 whose emitter 34 is connected to ground. Resistors 27, 29 and 62 are in series with each other and these resistors form a voltage divider for gate 26 to assure that the reverse bias voltage across the gate 26 and anode 22 is not above: the specified maximum value for the SCR used when transistor 32 is conductive. Resistor 29 thus serves to limit the current to gate 26 of SCR 20. A diode 60 is also in series with resistors 27, 29 and 62 and serves to effectively disconnect gate 26 from power lead 28 when transistor 32 is nonconductive and when a capacitor 36 connected to one end of primary winding 12 receives an actuation pulse from primary winding 12, capacitor 36 also being coupled to the junction of resistors 27 and 29. As a secondary function, resistors 27, 29 and 62 limit the current flow through transistor 32 when the latter is conductive.

As will hereinafter be set forth, gate 26 of SCR 20 will be reverse biased when transistor 32 is conducting to inhibit current flow through SCR 20, whereby opening of switch 18 to cause the collapse of the magnetic field of the coil will cause a voltage to be induced into the secondary winding, resulting in a current flow therethrough and thereby a spark discharge at one of the spark plugs of the engine. On the other hand, if transistor 32 is nonconducting, gate 26 will be forward biased by the discharge of primary winding 1.2 through capacitor 36. This forward bias will be great enough to permit SCR 20 to fire" and conduct and thereby allows the energy stored in the coil to be dissipated, when switch 18 is opened, through the resistance of primary winding 12 and SCR 20 rather than being inductively transferred to the secondary winding.

When transistor 32 is nonconductive and as switch 18 closes, gate 26 of SCR 20 is, in essence, floating since diode 60 and collector 30 are open. If switch 18 is then opened, the voltage at terminal 13 of primary winding 12 rises rapidly from the initial voltage level of the positive terminal of the battery until the charging current through capacitor 36, resistor 29, gate 26, anode 22 and the other terminal 11 of primary winding 12 causes SCR 20 to fire." When this occurs, the voltage at terminal 13 immediately swings back to a positive voltage somewhat higher than that of the positive terminal of the battery and capacitor 36 discharges at a rate determined by re sistor 29. Primary winding 12 then discharges its energy, at a rate determined by its resistance, through SCR 20 until .the current flow decays to less than a specified holding value" at which time SCR 20 returns to its normal open" state. The time constant represented by the parameters of resistor 29 and capacitor 36 is very much less than the R/L time constant of primary winding 12 so that there is no forward bias voltage on gate 26 when the current through SCR 20 decays to the aforesaid holding value.

The control means for controlling the bias voltage on the base of transistor 32 includes a first bank of PNP transistors 38 and a second bank of NPN transistors 40, each of these transistors having a current-limiting resistor 42 connected to the base terminal thereof. The resistors are in parallel with each other and are connected to respective terminals of a keyreceiving connector broadly denoted by the numeral 44 and having terminals denoted by A through R. These terminals are adapted to make electrical contact with respect to certain terminals 46 on a key 48 capable of being inserted into connector 44, the function of which is to actuate the control means, when properly constructed, so as to cause transistor 32 to be conducting and thereby allow an induced voltage in secondary winding 14 each time switch 18 is opened.

Transistors 38 are cascaded so that the emitter terminal of one transistor is connected to the collector terminal of the next adjacent transistor. This is shown in FIG. 1, for instance, wherein the emitter terminal 50 of one transistor 38 is connected to the collector terminal 52 of the preceding transistor, the emitter 54 of the transistor 38 corresponding to terminal B being connected to a current-limiting resistor 56, to a Zener diode 58, and to lead 28. The Zener diode is connected to ground and serves to maintain the voltage on lead 28 essentially constant. Lead 28 also connects emitter 54 with a resistor 39.

The transistor 38 corresponding to terminal Q of connector 44 has its collector terminal 64 connected to emitter 66 of PNP transistor 68 whose collector 70 is connected to a pair of resistors 72 and 74 in series, resistor 74 being connected to ground. The base 76 of transistor 32 is connected to the junction between resistors 72 and 74, emitter 34 of transistor 32 being connected to ground. The second bank of transistors 40 are cascaded in the manner similar to that of transistor 38, the collector 78 of the transistor corresponding to terminal P of collector 44 being connected by lead 86 through resistor 56 to lead 28. The emitter of the last-mentioned transistor 40 being connected to the collector of the transistor 40 corresponding to terminal H and so on, emitter 80 of the transistor 40 corresponding to terminal P of collector 44 being connected to ground. The base 82 of transistor 68 is connected to a resistor 84 which is, in turn, connected to lead 86 connecting collector 78 with resistor 56.

Power is supplied through lead 96 to terminal 90 and fuse 114 during starting operation by a starter relay connected to terminal 90 through a diode 97. Terminal 90 is connected by lead 94 to terminal R of connector 44 and also to resistor 39. To connect the output of an alternator or generator to the circuit, the output leads 99, 101 and 103 are connected through diodes 104 to lead 94.

Key 48 has a lead or conductor bar 108 (far side) connecting terminal A of connector 44 to the terminals 46 which are to be connected to those terminals of connector 44 coupled to transistors 38. For purposes of illustration, terminals 461), 46c, 46d, 46c, 46 j and 464 are provided on key 48 to contact terminals B, C, D, E, J and Q. Thus, these last-mentioned terminals and thereby the base terminals of corresponding transistors 38 are connected to terminal A and thereby to ground when key 48 is coupled to connector 44. In a similar manner, lead or conductor bar 106 (front side) connects terminal 46r to terminals 46f, 46h, 46k, 46m, 46n and 46p. Terminal R is connected to the positive side of the starter relay or alternator rectifier output so that the terminals F, l-LK, M, N and P and thereby the base terminals of corresponding transistors 40 are placed at positive supply potential.

The control circuitry described above may be connected by cable to the engine or vehicle with which coil is associated. For purposes of illustration, the elements of the invention are shown in an electrical schematic form in FIG. 2 wherein cable 65, connector 44 and key 48 are remotely located relative to lock assembly 56. Breaker point switch 18 is connected to the negative terminal of lock assembly 56 and the three-phase output of alternator 112 is connected by lead 99, 101 and 103 to the respective rectifier terminals of lock assembly 56.

Ballast resistor 16 is connected by means of fuse 114 to the positive supply terminal 90 of lock assembly 56. A conventional ignition switch 116 operated remotely from coil 10 is connected to the starter relay 118 and an ammeter 120. Ignition switch 116 and the combination of connector 44 and key 48 cooperate to cause actuation and continued operation of the ignition system. In the absence of one of these components or revision of any wires, the ignition system cannot operate. Starter 124 is connected to relay 118 and to battery 88.

Alternator 112 for use with this system is slightly modified with respect to a conventional alternator in that the threephase output thereof is connected from within the alternator. A key feature of the alternator connection is that the circuitry of the invention are powered from the alternator alone and are only powered from the battery during starter operation. This feature makes it possible to pull key 48 and stop the engine immediately. Moreover, it is possible to use the invention with an older model electrical system using a DC generator. In such a case, leads 99, 101 and 103 would be connected together and to the output terminal ofthe generator.

The circuit components are preferably attached to an etched circuit board molded in plastic in a form to fit on the tower end of a conventional ignition coil. Alternately, the circuit board can be molded integrally with the coil on any coil structure. If separately attached, the circuit assembly is preferably secured by tubular screws with a round or conical head and a one-way driving recess used to attach the circuit board to the coil terminals 1 1 and 13 and the wire connections 15 and 17 to the coil. The coil may be secured to the engine block with a padlock for additional security.

Key 48 is preferably made from a plastic sheet laminated on both sides with suitable conducting material, such as copper or the like. The key is preferably cut to approximately the size of a credit card and both sides are etched to form terminals 46 and conductors 106 and 108 connected to these terminals. This can be accomplished by making in one side of the key the high voltage side and the other side of the key the low voltage or ground side. Connector 44 accomplishes the function of interconnecting both sides of key 48.

Key 48 is made as a blank with all terminals 46 connected on both sides by conductor bars to conductor bars 106 and 108. Each conductor bar for each key face for a terminal 46 and has a drill target 47 in its center and encoding is accomplished by drilling a hole in the key at the target location. This results in an open connection since it severs only that conductor bar. The holes are shown in FIG. 1, wherein the bases of the PNP transistors are connected to conductor bar 108 and the bases of the NPN transistors are connected to conductor bar 106 when key 48 is inserted into connector 44.

Key 48 is also mechanically coded by means of a slot, such as the slot corresponding to the G terminal of connector 44. A tab is provided in connector 44 for insertion in the slot, thereby preventing keys with slots in other locations from being inserted in connector 44.

There are a large number of different ways in which the lock assembly 56 can be encoded and the encoding of the lock assembly will be determined by the transistor arrangement in two transistor banks. There is a fixed number of transistors, for instance, six PNP and six NPN transistors as shown in FIG. 1. Each of the transistor input positions can terminate in either a PNP or NPN transistor but not both. The coding possibilities are accomplished on the etched circuit board by making both transistor positions share the same base terminal connection and by installing a short at the collector to emitter etched board terminations on the unused transistor bank. Thus, position 128 (FIG. 1) provides an alternate possibility for locating a PNP transistor, replacing an existing transistor 40 in connector position N. Similarly, position 130 aligned with the NPN transistors provides another location for an alternate NPN transistor to provide a different coding arrangement, replacing a transistor 38 in the connector position J.

To change this arrangement, circuit board for the circuitry of this invention will be provided with alternate positions or locations 128 (shown in dashed lines) for rearranging the type of PNP transistors 33 or NPN transistors 40 for each command line. In the example shown, there are 12 transistors of which there are n PNP transistors and l2-n NPN transistors. Only one of the two possible positions is used for each transistor.

In operation, connector 44 is coupled to the transistor banks through resistors 42 and starter relay input is connected to terminals 90 with terminal 92 grounded. The alternator three phase output is connected by leads 99, 101 and 103 through diodes 104 to terminal R and ignition coil is coupled to SCR 20. It is assumed that key 48 is properly encoded so that negative voltages will be applied to transistors 38 whereas positive voltages will be applied to transistors 40 when the key is coupled to connector 44. The connector may be suitably formed so that it has a recess to receive the key.

When the key is out of the connector, transistors 38 and 40 are nonconducting so that transistor 32 is nonconducting. This is because base 76 of transistor 32 is at ground potential so that the transistor is off but not back biased. In this case, capacitor36 coupled to gate 26 charges whenever switch 18 opens. This charging of the capacitor forward biases gate 26 of SCR 20 so that when the switch 18 opens, SCR 20, which is conducting because of the forward bias on gate 26, provides a closed circuit with the primary winding allowing the energy of the collapsing magnetic field to be dissipated through the resistance of the primary winding and SCR 20. There will be a low induced voltage in the secondary winding so that there will be insufficient voltage produced to cause a spark to be discharged at the terminal of a corresponding spark plug.

Without the presence of key 48 in connector 44, the engine associated with ignition coil 10 cannot be started or operated. It will be necessary to provide the proper reverse bias on SCR 20 before such operation can be started and continued.

If the key with the proper terminals thereon is inserted in connector 44, negative or ground voltages are applied to the base terminals of transistors 38 and positive potentials are applied to the base terminals of transistors 40. The transistors are then forward biased and since they are connected to power lead 63, they become conducting. Since transistors 40 are conducting, this provides a forward bias on transistor 68 which becomes conductive because transistors 38 are conducting. This causes base 76 of transistor 32 to be forward biased since it will then be at a potential above ground due to resistor 74.

When transistor 32 conducts, this places a relatively low bias voltage on gate 26 of SCR 20, rendering the SCR nonconducting so long as transistor 32 coriductsThus, a voltage will be induced in the secondary winding 14 when breaker 18 opens since there is no closed circuit path for dissipating the energy of the collapsing magnetic field.

Since the displayed circuit assumes addition of the control to an existing vehicle, ignition switch 116 will be closed when key 48 is inserted in connector 44. The existing ignition key may be modified to make it impossible to remove from the ignition switch.

While the invention has been shown for use as controlling the energy transfer between windings of an ignition coil, it is clear that the invention can be used for other purposes as well. it can be used where a bias voltage is needed or where a par ticular current flow is necessary. In essence, transistor 32 operates as a gate to permit or prohibit operable structure.

The circuitry of the present invention can be considered an enabling or a disabling device in the sense that it allows or enables an event to occur or prohibits such event from occurring, in the latter case it disables a particular system. When applied to the foregoing apparatus, it enables the primary winding 12 to transfer its energy to the secondary winding to thereby induce a voltage in the latter. Thus, when transistor 32 is conductive, the combination of SCR 20 and primary winding 12 is in the enabling state. However, such combination may or may not have been actuated. When the combination is actuated (when breaker switch 18 opens), coil 10 goes through its firing operation as if SCR 20 did not exist. If transistor 32 is nonconductive, the combination or SCR 20 and primary winding 12 is disabled. When this occurs, and before the started sequence advances to a firing point, gate 26 of SCR 20 has a voltage approximately equal to that of lead 28 due to leakage so that SCR 20, up to that time, will have done nothing. When breaker switch 18 opens, the SCR and the coil form a closed circuit to cause the stored energy of the coil to be absorbed in the circuit rather than transferred inductively to the secondary winding. Thus, the energy is diverted from the second winding and dissipated in the form of heat.

In summary, the coding input actuates transistors 38 and 40 which, in turn, actuate transistor 68, the latter, in turn, actuates transistor 32 and this transistor enables the primary winding 12. Moreover, capacitor 36 provides a control member for SCR 20 when transistor 32 is nonconductive in that the capacitor, being responsive to the rate of voltage rise across coil 10, becomes charged when switch 18 is opened to thereby provide the forward bias voltage for SQR 20 sufficient to cause it to fire" and thereby be conductive. When transistor 32 is conductive, capacitor 36 is also conductive but it does not bias the gate of SCR 20 sufficiently to overcome the reverse bias or enabling voltage" caused by the conductive state of transistor 32.

The circuit of the invention shown in FIG. 1 has built-in safeguards to prevent tampering with the circuit so as to bypass the same. For instance, the transistor 32 and diode 60 can be selected to withstand a voltage of three times or more than the normal supply voltage and. to exhibit a small enough leakage current in the case of diode 60 or a small enough open state leakage current in the case of the transistor 32 so that either the transistor 32 will absorb most of the positive voltage impressed on terminal 11 (if lead 96 is removed from terminal or diode 60 will absorb most of the supply voltage (if terminal 92 is disconnected from ground and terminal 90 is grounded). This feature is possible due to relative high leakage current of reverse bias gate-anode junctions of available SCRs. The function of this protection is to prevent an intruder from connecting a higher voltage source to fuse 114, disconnecting wire 17 from the breaker, and manually grounding the disconnected wire to attempt to destroy the SCR 20 by burning the relatively sensitive gate 26 open by excessive applied reverse voltage and thereby permit unauthorized operation of the ignition coil after reconnection.

lclaim:

1. In combination: an inductive member; a silicon controlled rectifier device having a gate and adapted to be placed in an enabled state when a reverse bias voltage is applied to the gate, said device being normally ina disabled state and being connected to said inductive member to provide closed electrical current path therefor when the device is in said disabled state; a normally nonconductive, current-carrying member having means responsive to a predetermined electrical signal independent of the current through the device for rendering the current-carrying member conductive, said current-carrying member being coupled to the gate of said device for providing the reverse bias voltage therefor when the current-carrying member is conductive; means coupled with said gate for applying a forward bias voltage to the gate when said current-carrying member is nonconductive to thereby place said device in said disabled state; decoding means having a plurality of actuatable, current-carrying elements for generating said signal when the elements are simultaneously actuated; means connecting said decoding means to said signal responsive means of said current-carrying member, whereby the latter becomes conductive when said signal is generated; and means coupled to said elements for simultaneously actuating the same.

2. Control apparatus as set forth in claim 1, wherein said current-carrying member comprisesa transistor, means including a voltage divider for connecting the transistor to said device, said voltage divider providing said enabling voltage when said transistor is conductive.

3. Control apparatus as set forth in claim 1 wherein said decoding means includes a connector having a plurality of terminals, a group of PNP transistors, a number of NPN transistors, and a power source having a positive terminal and a negative terminal, the base of each of said transistors being connected to a respective terminal of said connector, said ac- 'tuating means-including a for coupling each terminal. of

the connector to a respective terminal of the power source.

4. in combination: an inductive member; a silicon controlled rectifier device havinga gate and adapted to be placed being connected to said inductive member to provide closed electrical current path therefor when the device is in said disabled state; -a normally nonconductive, current-carrying member having means responsive to a predetermined electrical signal independent of the current through the device for rendering the current-carrying member conductive, said current-carrying member being coupled to the gate of said device for providing the reverse bias voltage therefor when the current-carrying member is conductive; a capacitor coupled with said gate and with said inductive member for applying a forward bias voltage to the gate when said current-carrying member is nonconductive to thereby place said device in said disabled state; decoding means having a plurality of actuable,

current-carrying elements for generating said signal when the elements are simultaneously actuated; means connecting 'said decoding means to said signal responsive means of said current-carrying member, whereby the latter becomes conductive when said signal is generated; and means coupled to said elements for simultaneously actuating the same.

5. The combination as set forth in claim 4 wherein said inductive member has a pair of ends, said device having a pair of terminals connected to respective ends of the inductive member, said capacitor being connected to one end of the inductivemember and to the gate of said device.

6. The combination as set forth in claim 5, wherein said current-carrying member includes a transistor having a base defining said signal responsive means.

7. The combination as set forth in claim 5, wherein said cur rent-carrying member comprises a transistor having a collec- 

1. In combination: an inductive member; a silicon controlled rectifier device having a gate and adapted to be placed in an enabled state when a reverse bias voltage is applied to the gate, said device being normally in a disabled state and being connected to said inductive member to provide closed electrical current path therefor when the device is in said disabled state; a normally nonconductive, current-carrying member having means responsive to a predetermined electrical signal independent of the current through the device for rendering the current-carrying member conductive, said current-carrying member being coupled to the gate of said device for providing the reverse bias voltage therefor when the current-carrying member is conductive; means coupled with said gate for applying a forward bias voltage to the gate when said current-carrying member is nonconductive to thereby place said device in said disabled state; decoding means having a plurality of actuatable, current-carrying elements for generating said signal when the elements are simultaneously actuated; means connecting said decoding means to said signal responsive means of said current-carrying member, whereby the latter becomes conductive when said signal is generated; and means coupled to said elements for simultaneously actuating the same.
 2. Control apparatus as set forth in claim 1, wherein said current-carrying member comprises a transistor, means including a voltage divider for connecting the transistor to said device, said voltage divider providing said enabling voltage when said transistor is conductive.
 3. Control apparatus as set forth in claim 1 wherein said decoding means includes a connector having a plurality of terminals, a group of PNP transistors, a number of NPN transistors, and a power source having a positive terminal and a negative terminal, the base of each of said transistors being connected to a respective terminal of said connector, said actuating means including a key for coupling each terminal of the connector to a respective terminal of the power source.
 4. In combination: an inductive member; a silicon controlled rectifier device having a gate and adapted to be placed in an enabled state when a reverse bias voltage is applied to the gate, said device being normally in a disabled state and being connected to said inductive member to provide closed electrical current path therefor when the device is in said disabled state; a normally nonconductive, current-carrying member having means responsive to a predetermined electrical signal independent of the current through the device for rendering the current-carrying member condUctive, said current-carrying member being coupled to the gate of said device for providing the reverse bias voltage therefor when the current-carrying member is conductive; a capacitor coupled with said gate and with said inductive member for applying a forward bias voltage to the gate when said current-carrying member is nonconductive to thereby place said device in said disabled state; decoding means having a plurality of actuable, current-carrying elements for generating said signal when the elements are simultaneously actuated; means connecting said decoding means to said signal responsive means of said current-carrying member, whereby the latter becomes conductive when said signal is generated; and means coupled to said elements for simultaneously actuating the same.
 5. The combination as set forth in claim 4 wherein said inductive member has a pair of ends, said device having a pair of terminals connected to respective ends of the inductive member, said capacitor being connected to one end of the inductive member and to the gate of said device.
 6. The combination as set forth in claim 5, wherein said current-carrying member includes a transistor having a base defining said signal responsive means.
 7. The combination as set forth in claim 5, wherein said current-carrying member comprises a transistor having a collector, and wherein is included a power source, and means connecting said collector to said power source. 